Grate soap until fine. I like using a food processor, but a regular cheese grater will do. If using a processor, I put a little bit of the Borax or the washing soda in first. It helps process the soap.
Mix in Borax and washing soda.
Put in a container and use one tablespoon per load.
Recipe by Scratch or Sniff at http://www.scratchorsniff.com/soapbox-diy-laundry-detergent/